Leakage compensator for hydraulic systems



June 25, 1935. H. ERNST ET AL 2,006,311

l LEAKAGE COMPENSATOR FOR HYDRAULIC SYSTEMS 4 Fi1ed sept. 9, 1931 e sheetsfsheet 1 June 25, 1935. H. ERNST Er AL l 2,005,311

LEAKAGE CMPENSATOR FOR HYDRAULIC SYSTEMS Filed Sept. 9, 1931 6 Sheets-Sheet 2 Snowdon `lune 25, 1935. H ERNST ET AL V2,006,311

LEAKAGE coMPENs'AToR FOR HYDRAULIC SYSTEMS Filed sept. 9. '1931 6 sheets-sheet :s

@51g @Mom/wif I June 25, 1935. H. ERNST Er AL LEAKAGE COMPENSATOR FOR HYDRAULIC SYSTEMS Filed sept. 9; 1951 `e sheets-sheet 4 EQ EN @vmm n@ wm nvamtou WW M.

55% www# /ma June 25, 1935. H. ERNST Er A1,. 2,006,311

LEAKAGE coMPENsAToR FOR HYDRAULIC sYsTEMs- Filed sept. 9, 1931 e sheets-sheet 5 June 25, 1935. H. ERNST Er AL 2,006,311

JLEAKAGE COMPENSATOR FOR HYDRAULIC SYSTEMS Filed Sept. 9, l1931 6 SheetS-Shee'cl 6 vwentou 3513 abme/134- Patented June 25, 1935' UNITED STATES PATENT OFFICE LEAKAGE coMPENsA'roR Fon HYDRAULIC` l l SYSTEMS Hans Ernst and Bernard Sassen, Cincinnati,

Ohio, assignors to The Cincinnati Milling Machine Company, Cincinnati, O hio, a corporation of Ohio Y Application September 9, 1931, Serial No. 561,900

26 claims.

This invention is directed to the remedying of:

.istics which, through a long process of development, have been rendered of exceptional value in many environments of whichvthe machine tool art is an outstanding example. This application has become extensive despite the inability to Aolotain, or maintain, a desired close adherence be-' Even if it were possible, through the exercise of the utmost care and rened machining methods, to produce an operative hydraulic power device with itsA relatively moving parts free oi leakage, sch would be without the range of practicability. `It is a recognized fact that leakages are unavoidable in commercial machines, and that these leakages are of .such amount as to very materially affect the operation of the machine. Under a given temperature and pressure condition the graduations associated with the control element of any specic machine can, of course, be modified to correctly indicate the observed'actual speed irrespective of the leakages.- However, this would be of little value since such indication would be correct for only the particular temperature and pressure selected. This follows from the'facts rst, that the discharge through an orice of a given area (leakage area) vvaries. as the fluidity (inverse of viscosity) which varies as the temperature ofthe liquid; and second, that the discharge varies as the pressure difference. Insofar, as this discussion is concerned and for practical purposes it may be considered that the variation is in ydirect proportion tothe pressure difference across the orice; and likewise bears a deniterratio to thevuidity. Each of these properties varies through a considerable range in any specic system. A liquid which has been forced through a series of throttle valves and various apertures for a substantial period of time attains a temperature far exceeding that of the liquid in a col machine. Likewise the pressures may vary through an exceedingly wide range dependentV upon the work resistance. 'A .Such values, e. g., as 0 t0 1000 lbs. per squareinch are very common. f A

In attacking the problem of correcting or compensating for the various leakages under these (cl. 'sofsm varying conditions and for all types of hydraulic systems, it has been found that the various systems can be advantageously classied under two general headings vin accordance with an opposite, but in each case, dominant characteristic thereof.

- Such classification is:

A: 'I'hose in which the feed rate controlling device regulates the discharge of'uid from the motor, and f lB: lThose in which the feed rate controlling device regulates the supply of vfluid to the motor.

In either of these cases, however, there are two kinds of leakages which materially affect the feed ratehleakage of fluid out of the control lines to points of lower pressure; and leakage ofuid into the control lines from points of higher pressure. While the causes of such leakages are the same in either system, the eiiect of the leakages are dilerent. In an hydraulic system in which the rate control mechanism governs the supply Huid to the motor, leakage of iluid ou of the supply linesproduces a retarding eiect upon the feed rate, while leakage of fluid in produces an advancing effect upon the feed Arate. The converse occurs in a type of system inwhich the rate controlI mechanism regulates the discharge of fluid from the' motor, to wit, leakages out of the control lines tend to advance the rate of travel, while leakages in the control lines tend to retard the rate of travel 4of the machine element.

Regardless ofwhich system is used, the effect of the leakages upon the feed rate, for Vany given set of conditions, may present any one of three possibilities, firstly, that the leakage in exceeds the leakage out; secondly, that the leakage out is in excess of the leakage in; or thirdly, that'the leakage in equals the leakage ou Since the last mentioned case would be of rare occurrence, and further would normally obtainl for even the same system under one specic set of pressure conditions only, it may be considered for all practical purposes every system falls within one of the other two classes. As to these other two types of cases, a variation of any one or more of the conditions such as variationsof Vtemperaverting Ythe minor leakages (-in or out) into the major leakages.` In other wordsa given machine which operates at a speed in 'excess of the. indicated speed under one set of conditions may loperate Vat a speed less than the indicated one under adifferent set of conditions, or a different speed adjustment. Many factors may contribute to producev the foregoing described variations. It may be noted, for example, that pressures at certain points in the system may vary as the work resistance but not at the same rate. Also at a particular leakage area, though large, the leakage may be small in amount and constitute a small factor in the summation of leakages. However, for a different work resist` ance the pressure difference across this particular area may become relatively high and it then becomes a major factor in the total leakages. These characteristics will become more apparent' from the consideration of any particular mechanism such as those noted hereinafter.

A condition which may be present in many circuits is that of a, negative work resistance. Normally work is considered as offering a positive resistance to table movement. However, the reverse of this may be true. There may be a mechanical force e. g. urging the piston forward in the direction of feed which requires a resisting hydraulic pressure in the back line in excess of that in the forward line. Obviously, the leakages may be pf entirely different character when a machine is operating under a negative resistance from those occurring when operating under a positive work resistance.

Certain types of milling machines offer an outstanding example-of conditions to be met in this respect. cutting tool may be rotating in a direction directly opposed to the relative feed between it and the work-table. However, the extreme reverse of this condition occurs when the cutting tool is rotating in the opposite direction with a hook-in cut acting to urge the translatable element in the same direction as the feed. K

For any substantial cutting force the forward 'urge acting on the table will exceed the resistance to table movement and the back pressure on the pistonexceed, therefore, the forward pressure. We have, then, the condition of a negative" work resistance. A condition of this nature obviously requires a resistance to the discharge of fluid from the back line. Such a resistance forms a concomitant of the discharge regulated type of system and this type of system, most completely described herein, affords an illustration of the universal adaptability of the present invention.

As the work resistance varies from positive to negative, the pressures on opposite sides of the piston simultaneously vary, but inversely, with the pressure on the back line becoming greater than that on the forward line. The leakages correspondingly vary and, in fact, the leakages between the forward and backvlines reverse in direction. This specific example illustrates the variations in leakages which may occur, including a case in which the in leakage may become an out leakage and conversely, dependent upon which side of the motor the rate control line is located. y

In its broadest aspects the means employed for satisfying this complex problem involves the fundamental principle f maintaining an automatic balance in the rate control line between the total advancing leakage, and the total retarding leakage, atall values of work resistance, and accordingly at all operating pressures. The invention proposes the introduction into the system of artificial leakages, the total of which, combined with the natural leakages of the machine, result in a balance thereof; i. e.v the summation of leakages, to which the rate control .line is subject/ed, are

' exists.

Under one condition of operation the` made to equal zero. This artificial leakage may assume the aspect of an injection of fiuid into, or an extraction of fluid from, the rate control line. Also the artificial leakage may be that produced by one or more leakage devices` which automatically vary the amount of compensating fluid;1

or .it may be the result cfa more or less fixed artificial leakage associated with a variable artificial leakage. The variations in artificial leakage may be produced by variations in pressure across the artificial leakage areas; or by variations in the leakage areas. All of these more specific aspects will be made more apparent from the discussion hereinafter in connection with the drawings.

A notable characteristic of a type of circuit, like those referred to above, is the fact that the pressures at certain points in the working system bear a definite relation to pressures at other points therein. As the pressure at one point varies, the pressure at certain other points simultaneously varies. The variation may be inversely or directly proportionate but the relation Further, such variations bear a distinct relation to the variation in work resistance from the extreme negative Value to the extreme positive value within the range of the machine. This relation is taken advantage of in the present invention in automatically producing the proper amount of compensation. Through the incorporation in the circuit of one or more devices for enforcing an artificial leakage over the natural leakage, and causing this artificial leakage to likewise vary directly or indirectly as the pressure at some critical point in the system a continuous balance is accomplished.

A particularly noteworthy characteristic of this method of compensation is, that once a balance has been effected under a certain temperature this balance will remain substantially undisturbed under changes in temperature, since leakages-in and leakages out across the respective areas will vary simultaneously in accordance therewith. A balanced system as thus devised is not only free of disturbance of changes in temperature of the particular hydraulic medium for which it was adjusted; but is unaffected, insofar as the ultimate balance is concerned, by the substitution in the system of an oil of a higher or lower viscosity from the original fluid at a given temperature. The same is true if the characterfluid is a factor of considerable importance, it

will be apparent, from a practical standpoint.

In arriving at this point in the disclosure of the invention it is to be noted the compensation in this manner involves also the utilization of the phenomena heretofore referred to-that ,-for practical purposes it may be considered that leakage, through the areas encountered in these devices, will vary as the temperature of the fiud; as the pressure difference across the area; and as the area changes in value. In accordance with these desiderata and principles upon which the accomplishment of the objects hereof are achieved an initial step in the application of the invention in a specific machine or type of ma chine is to determine its leakage characteristics. This may be conveniently doneby selecting some critical but stable condition, such as the operation under idling conditions and selecting and recording the proper data. This is done for one temperature of the liquid; and then repeated for a different temperature. By means of a simple known method of calculation which involve's the values of forward and back pressures and the "calculation of lthe feed rate which would be obtained when the leakages are vmade equal. A device is then introduced into the system and adjusted until the actual feed rate equals the calculated feed rate. selected, the summation'of the leakages or the resultant effective leakage is zero, and the`system is now balanced. 'With the adjustment made, the pressure differences will remain the same and the machine will remain substantially balanced, during idling, irrespective of changes in temperature since all leakage across the vari.,

ous areas will vary simultaneously and in proportion to the temperature changes. With, however, a change in work resistance, the pressure differences will change. These changes may not be, and usually are not, to the same degree. Frequently, they are not in the same direction. They will, however, all bear a definite relation to the changes in the work resistance as heretofore noted and by providing a compensating leakage means, which is responsive to variations in pressure at some'critical 'point inthe circuit, and which varies in the correct direction, the compensation for leakage will be correct for all working conditions.

The individual leakages throughout the system bear a simple relation to the pressure changes and, in fact, in most cases are depictable graphicallyL as a substantially straight line curve.

'I'he summation of the'leakages, omitting the" artificial variable compensating leakage, also assumes values expressible as a simple curve.

The required variable compensating leakage will be, therefore, a curve of like nature. It becomes possible then to provide a valve device which is so arranged as to produce a compensating dischargewhich correspondsto values indicated by such a curve.

Fora more complete disclosure of. the manner of compensating for leakages.and maintaining a balanced system reference may be made to the hereinafter detail description and the ,accompanying drawings wherein are disclosed'typical adaptations of both the basic'and the more specic aspects of'this invention. In the drawings' like characters of reference denote lcorresponding parts throughout the various views of which:

Figure 1 is a diagrammatic view illustrating a' simple circuit of the supply regulated type; Fig. 2 likewise depicts anelementary'circuit but of the discharge regulated type. Fig. 3 is similar to Fig. 1 with the incorporation therein of a variable opening leakage valve; Fig. 4 corresponds .to Fig. 3 with the addition of pump means to provide a super-pressure; Fig. 5 shows an arrangement to provide a constant pressure difference across the leakage valve; Fig. 6 is similar to Fig. 2 but with the articial leakage device made responsive to the forward pressure instead of the back pressure as' in Fig. 2; Fig. 7 depicts an elementary circuit which provides compensation in a somewhat different manner from the preceding ones; Fig. 8

'is similar to Fig. 7 but with the variator made responsive to variations in pressure in the forward line; Fig. 9 shows in more complete but somewhat diagrammatic form an entire circuit including the For the condition (idling) l Fig. 11 shows a complete circuit in which compen-. y

sation for leakage is also provided under conditionsof a negative work resistance; and Fig. 12 discloses a system for accomplishing in a different manner the balancing of leakages under conditions of vboth positive and negative work resistance, the variator in this case being a valve of a single continuous curve. I

The two'l general classes of hydraulic system, distinguished accordingto supply or dischargev rate control, are depicted in elemental and diagrammatic form in Figs; l and 2. Likewise these two figures illustrate in a simple manner a fundamental conception of the desiderata of vcompensation for leakages forming the subject of this application. v

No attempt is made in these preliminary diagrammatic figures, to illustrate the various leakage points. Although leakage across the'piston is, in a large proportion of the cases, the most obvious one, there are, nevertheless, innumerable other' places such as various valves, pumps, metering devices, and joints both in the forward and in the back line which present areas likewise susceptible to leakage dependent upon the particular system.

In Figure 1 the rate controlling member T regulates the supply of fluid to the motor M; whereas Fig. 2 villustrates a system in which the rate controlling mechanism T1 regulates the discharge of fluid from-the motor. In these initial figures, the

regulating devices T and T1 are shown without de- -I tail'of internal construction. It is to be borne in mind, however, that the illustrations herein are, in the interests of simplicity, mainly diagrammatic, and such devices may assume varied forms well known in the art for positively governing the l l for such specific leakages it is contemplated thatv the means provided herein are designed to likewise compensate for those speciflc'leakages. In

general, in referring to the rate control line, the regulating device is included as part thereof. For

of the positive displacement type is employed. A

primary characteristic of these rate controlling devicesis that of a positive adjustment' of the rate -f vfluid movement, in association with some form of graduated scale to indicate the selected rate of feed. ',InFig. 1 -a pointer I connected to the manual adjustment for the regulating device T moves adjacent a graduated scale 2.

In accordance with the objectives of this description to disclose the principles of thev invention withoutthe introduction of unnecessary mechanical detail, the power device M is depicted in one of its simplest forms as 'a plain cylinder with reciprcatory piston. valve mechanism for reversing and stopping the motor is omitted since with a general understanding of the principles of the invention derived from Likewise all distributingA detail consideration` of these matters hereinafter. With respect to leakages, in the case of Fig. 1, it

will be noted that leakage of fluid out of the rate control line 3, decreasesv the quantity going to the motor and retards the rate while leakage of fluid in to the rate control line' increases the supply to the motor and advances the rate of movement.

Under the conditions of a positive resistance to movement of the table W carrying the work W1, resulting when cutter C is rotating clockwise and 4 the table is being fed to the right, the pressure in line 3 must be greater necessarily than the pres'- sure in line 4. As a consequence there will be a retarding leakage from line 3'to line 4 in quantities determined by the pressure difference and total areas of the oriilces through'which this leakage can occur. Similarly, under the same condi- -f tions, with the system illustrated by Fig. 2, the

l fective leakage zero,

will, remain zero regardless of the temperature of pressure in line must be greater than that in line' 6 to eifect a movement ofthe table W, and there will result a retarding leakage from the forward pressure line 5 to the back pressure line 6. In the case of thedischarge regulated type of system of Figure 2 there also will be a leakage from the back pressure lines 6 tothe reservoir, which tends to advance the feed rate and if the leakage into the back pressure lines equals, or is made to equal, the leakage out of the back pres-l sure lines, the resultant effect of the leakage on the idling feed rate is reduced to zero. In practice it is usually found that one exceeds the other and compensation must be made for. the difference, and a device introducedv into the circuit which will afford the necessary compensation forv leakages.

Such a device may assume varied forms, the adjustable choke valve A1 and A2 illustrated in Figs. 1 and 2 lrespectively, .representing one form of device for compensating for the initial or natu-f ral leakage out of the rate control line of the system when the machine is operating under a specific condition such asthat of idling. In Figure 1 the valve plunger a is adjusted by screw b to determine a iiow of fluid from the supply line zI to the forward line 3. The amount of fluidV thus injected, forA any particular-machine, will be determined, of course, by suitable tests.

In Fig. 2 the valve A2 serves to inject fluid into the back line 6 from the forward line 5. If it is found that the leakage out of the back pressure line exceeds the leakage froml the forward pressure to the back pressure, complete compensation for idlingconditions can be produced through valve A2; but if itis found that the leakage from forward pressure to back pressure is fin excess of the leakage from back pressure to reservoir, then an additional compensation is made through ya second valve S2. By adjusting' the sleeve nut D of this valve the relationship between the valve plunger 8` and the holes in the valve'sleeve will be changed whereby an initial artificial leakage out of the back pressure line is'provided.

Once `the foregoing adjustments have been made, and which serve under idling conditions, it

the oil...However, `theleakages will vary under different cutting conditions, and in different machines in accordance with their respective charto make the resultant ef-v acteristics and in order to maintain a balance under all conditions further adjustments are made available in the valve S2.

Referring to the details of this valve, Fig. 2, it will be observed that it comprises an outer bored casing member 9 within which a sleeve member Il! is secured. lVlithin the sleeve is the 'slidable 1 valve piston 8, previously referred to, one end of which is acted upon byfluid pressure entering port II from the back pressure line 6 in opposition to an adjustable spring I2. Intermediate the ends of the valve plunger 8 is formed an inclined reduced portion I3 which offers a restricted passage to the flow of fluid through port I4 and out the port I5 to a point of lower pressure such as, in the instant case, tothe reservoir I6. Now, when the machine is idling, if the nut D is moved inwardly, toward the left in this iigure the plunger 8, spring I2 and screw I1 are all moved together so as to vary the relationship between the valve portion I3 and the holes in the sleeve I0 and which movement increases the amount of fiow out of the back pressure line. But if /the nut D be adjusted outwardly to the right, the flow will be decreased. The adjustment toward the left to provide an initial leakage through valve S2 is made only when the leakage, under idling conditions, from the forward pressure to the back pressure isv in excess of the leakage from the back pressure to the reservoir. v

Having established an initial balance of leakages under idling conditions, the valve S2 will also automatically function to compensate for leakages under conditions of added` positive work resistance. When the cutter C. is in engagement with the work and rotating in such direction as to impose a positive resistance to the movement of the work table vW, the pressure in line 6 will fall, and consequently vthe spring I2 will move the plunger 8 toward the left, thus increasing the flow from back pressure to reservoir, and thereby automatically compensating for the increased natural leakages fromlforward to back pressure lines due to the increased pressure difference.

Compensation for variation in conditions as e. g. lthe amount of leakage ori-different machines under working conditions, is made by adjusting the set screw I1. This adjustment varies lthe number of active coils of the spring I2 and in this way it is possible to vary thepressure required to shift the valve plunger a unit distance-by varying its spring characteristicwithout the necessity of substituting a spring of lin turn is dependent upon the fluid pressure exerted thereon. In addition, the leakage across the valve S2 is dependent upon the pressure difference which varies as the pressure in line 6.

Thequantity Q therefore becomes ja function of the square of the pressure in line 6, which de fines a parabola and graphically, or algebraically,

informs us that the contour` of the active por-1 tion of the valve member I3 should, for correct compensation, at all pressures, be parabolic.

` v2,006,311 Practice demonstrates, however, that by a slight departure from the ultima of construction, to Wit, making the valve portion conical instead of parabolic, a less expensive valve can be made and one which, for al1 practical purposes, provides suiiicicntly accurate compensation. v

For perfect compensation using a conical valve,- it would be necessary to make the pressure difference between back pressure and the outlet across valve S2 a constant amount in order that, instead of leakage taking place between the back pressure and the constant low pressure, the leakage takes place between back pressure'and a.'

pressure lower than back pressure by a constant fixed' amount. Such a system is illustrated diain line 22 by a xed amount, and thepressure differential 4across the leakage by-pass Valve S5 will remain at a fixed value. Under such conditions the only effective variable Yis the pressure variation in the back line acting on thev piston face 23 and the slope of the valve becomes a straight line function.

The regulating or rate control device exemplied by the mechanism designated T or T1 may operate in any of the Well known manners commonly employed, including manual or automatic means. In Fig'. 2, e. g. the adjustment is determined by the cam t rotatable with the gear t1 on the shaft t2. The member t3 can be assumed to be urged against the cam by' a suitable spring or other impositive means. `A rack t4 meshes with the gear t1, which rack may be operated either manually or automatically through association with an element 'novable in accordance with the machine cycle; e. g. a cam plate t5, adjustably carried by the work table W, which has been previously cut or contoured in conformity with the character of the Workpiece. t" is also illustrated for effecting manual adjustments to the throttle T1 or which may be set in a given position thereby to act as a limiting device for controlling'the maximum or minimum adjustment to be effected automatically to the rate control device T1.

In connection with Fig. 1 there was described the broad application of leakage compensation to a system of the supply regulated type. Figs. 2 is directed to a system of the discharge regulated type and provides for the contingency in- Which the Iinitial leakages into the rate control line during idling conditions are found to be in excess of the leakages out of the ratej control (back) line and the net leakages could not, 4therefore, be compensated for by the valve A2. In addition provision was made to compensate for variation in leakage resulting from variable working conditions with'v the: attendant uctuation in presures in the system.'v These additional factors,- it was shown, could be peculiarly well met through the incorpo-ration in the system of the shuttle valve S2.

In Figfl,l Y'it is shown how this same complete automatic leakage compensation can be effected in the first mentioned type of system referred to pipe 29a.

A second cam ts actuated bythe lever as the supply regulated type. If, under idling conditions, the natural leakages outof the rate control line 24 an1 in excess of the in-leakages, the initial adjustment therefor is made through a proper opening of the valve A3. Further compensatory artificial leakages to counterbalance increased leakages under working conditions are eiected through subjecting the variator ofy valve S3 to variations in pressure in the rate control line 24, in this case the forward line. This is accomplished through the application of fluid pressure to the Valve piston face 26 of the valve plunger 25, fluid being directed thereto through the pipe 21. Thus the same variations in pressure causing variations in leakage are utilized to correspondingly Vary the amount of compensating fluid.

In Fig. 1 a source of fluid under constant pressure was assumed for the line "I and which pressure was higher than that in line 3. The same is true with regard to lines 24a and 24 respectively of Fig. 3. In case this uid of higher pressure were not obtainable from the main supply line (24b of Fig. 3) a mechanism similar to that of Fig. 4 could be employed tol provide a super-pressure for the fluid to be injected. The, circuit 'of Fig. 4v

includes the regulator T andv valves A4 and S4 functioning in the same manner as the regulator T and valves A3 and S3 of Fig. 3. In Fig. 4, however, lan auxiliarysource, of higher pressure iiuid is provided through themediunr of pump B discharging into the line 28'. A differential valve -H is connected to line 28 in which the movable plunger h. is subjected tothe pressure, in one direction, 4of spring h2 as well as the' pressure in the forwardline 29f, whereas the opposed piston face of equal area is connected directly to the pump 4discharge line 28. Accordingly, the pressure inl the`latter line will be greater than that in theline 29f. Any excess fluid from the pump B will .be .discharged back into line 29, through Whiler Figure 4 indicates this source of higher pressure as an auxiliary device'it is ,to' remembered that the figure is essentially diagrammatic and normally the pump B may form a major element in the circuit such as the pump vBo employed in the circuits shown more comi pletely in Figs. 11 and 12.

While Figs. 2 and 5 e. g. illustrate uid connections and an arrangement for subjecting the shuttle valve or variator S to pressure changes in the back pressure; it is to be understood that,

in systems where theforward pressure varies simultaneously with variations in the work resistance and in the back pressure, the same artificial leakage means may be made responsive to changes in the pressure of the forward line; or

Assuming such a system as that just noted, as

thework resistance increases the forward' pressure increases and the back pressure simultaneously decreases. Accordingly there will be an increase in the natural leakage into the back line from the forward pressure line. is balanced by increased leakage across lvalve S6 as the valve is moved further to the right under The details However, this the action of the increased pressure in line 3|, and compensation is accomplished, therefore, as before. To compensate for the effects of leakages under idling conditions, a valve A6 which is adjustable to suit the leakage requirement may be employed to inject compensating fluid from the forward line into the back line. Y

Another type of system which approaches the problem of leakage compensation from a diiier-l ent angle is illustrated in Fig. '7. In accordance therewith an adjustable, but normally fixed or constant, artificial leakage area fromv the back pressure line 6 to the reservoir is provided through the valve K. In this case the valve K is adjusted to provide an articial leakage out of the back pressure line equal, at least, to the maximum natural or inherent leakage into the back line which would be encountered within the range of the machine. The latter normally would occur under maximum cutting resistance. In conjunction with valve K'a variable leakage device,'

responsive to working conditions, is introduced into the system to compensate for the conditions within the wide and usual working range wherein the cutting resistance is less than the maximum. This device is exemplied by the valve S" which is a form of the variator or shuttle valve heretofore considered. A primary function of the valve S7 is to bleed a variable amount of uid from the high pressure forward line 5 into the back pressure line 6. The position of the valve member, it will be seen, is a function of the back I plied.

The adjustable reaction member D provides an additional method of controlling theinitial leakage compensations.

Fig. 8 is a fragmentary view which, when considered with Fig. 7 discloses a. system similar thereto, but with the fluid 4connections altered such that the variable in-leakage valve S9 to the back pressure line is made responsive to variations of pressure in the forward line. Such means for automatically controlling the valve Sa is of course dependent upon the system being of a type described in connection with Fig. 6; and of which the arrangement shown in Fig, 9 is an example having its diiferential valve 5| which serves to maintain a definite relation between the rate of change in the forward and back' pressure lines as the Work resistance varies. In accordance With Fig. 8 uid is conducted from the forward line through a branch 35 to act on the piston face 36 of the valve member 31 against the force of the spring 36. The pipe 39 directs the by-passed :fluid into the back line. The valve opening, therefore,.varies inversely as the forward pressure; whereas in Fig. 7 it varies directly as the back pressure. But in each case the valve openving varies inversely as the Work resistance, and the compensating fluid injected .varies in.' 'like amounts with the variations in the natural leak;- ages.

A complete adaptation of the leakage compenyconnection with 9. Although this gure is likewise somewhat diagrammatic, the omitted details of automatic and manual control or operation can readily be supplied by one skilled in the art. If desired, reference may be made to British Patent #297,104 `of March 28, 1929 showing a complete organization of this natureA includingl typical actuating mechanisms.

All the essential elements of the hydraulic system are disclosed in Fig. 9 and comprise the power motor M which includes the piston 40 connected through the piston rod 4| to the work table W on which is mounted the work W1. A milling cutter is illustrated at C indicated as rotating in a counterclockwise direction.v Pipe lines 42 and 43 lead to opposite ends of the cylinder from th valve casing 44 in which is located the stop valve member 45. A selector valve L is connected to the valve casing through vthe single line 46 and the divided line 41. The'details of the stopvalve and of the selector valve L and the manner of their operation need not bev described here for the purposes of the present invention. Suiiice' it to state that the mechanism in question may be as shown in the British patent above referred to; or it may be any otherfmechanism capable of governing the supply and exhaust of uid with respect to the opposite ends of the motor M in accordance with a desiredcycle.

It will be noted in Fig. 9 and subsequent figures that a rod 4I' projects from the piston 40 inothe direction opposite to the piston rod 4 Il. With such an arrangement all variations or errors are eliminated which might result, under certain conditions of operation and pressures, when a diier-v ential piston is employed. In the more or less diagrammatic Figures 1 to 8 inclusive'this factor was not discussed particularly since these preceding iigures are intended to illustrate the broader aspects of the invention rather than its adaptation to universal conditions. Furthermore, it is to be noted that even with differential` piston areas involved, in a one-way feed machine where the stroke in one direction is entirely an idling stroke no error or departure from a complete balance of leakages, once properly established, would normally occur during the critical period when the regulated feed was effective. Also, in `any case where an error or variation of this nature might occur, the extent thereof would be dependent upon the comparative values of the differential piston areas, and in many instances where the piston rod e. g. is merely of such size as is required to, withstand the mechanical-forces, any error attributable to this factor, as a practical matter, may be neglected.

It is not to be overlooked, however, and due consideration must be given to the fact that in sistance, the pressure in pounds per square inch I in the forward line may be greater in one direction of movement than the pressure in the back line; whereas in the reverse direction of mover ment the pressure in the forward line may be less than in the back line.

The hydraulic circuit illustrated includes the rapid traverse pump RT which may be 'a gear pump adapted to supply fluid at a rapid rate through the line 48 and suitable ducts in the Valve 75 the particular conditions and purposes.

v change under changes in Work resistance.

tain in the forward line a sufliciently high pressure when called upon to meet the conditions of maximum pressure required. The pump VD', in its u'sual form in this type of circuit, is of the variable displacement type heretofore referred to. It will be seen that the system of Fig. 9 is of the type in which the rate of feed is determined through control of the rate of discharge of fluid from the back pressure line; and that th;` pump VD comprises the -means for so controlling the rate of discharge. The pump VD, in fact, functions as a meteringpump being one speciiicform of the means, for controlling the rate of flow, broadly referred to in connection with previous figures. As heretofore explained, andas shown in the British patent referred to, it is contemplated that this' metering device in whatever form employed has associated therewith, means for selectively adjusting it to provide any desired rate within its range and that normally required cf the machine, the adjusting means being employed in conjunction with a graduated indicator. Such an adjustment forms part of the details of construction disclosed in the said BritishV patent, and l The hydraulic system of Fig. 9 includes a differential valve 5I which may ormay not be employed in these various systems dependent upon 'Some form of means of this nature is essential, however, where automatic adjustment of the leakage lvariator is dependent for its functioning upon vvariations in pressure `in the forward line. Furthermore a differential valve means of thisgeneral nature forms an element in the particular type of commercially known hydraulic system adopted for illustration of our invention, and it becomes convenient to include it herein.` The piston area 52 of the slidable member 53 is .subjected through pipe connection 54 to thepressure in the back line. A tapered portion 55 is exposed to the pressure of the forward line through the` branch pipe 56 and controls the release of excess fluid from the forward line to the exhaust line 51. A spring 58 opposes the uid pressure exerted on the valve. The details bf valve 5| will be enlargedupon in connection with Fig. 10 but for the time being it maybe noted that it serves primarily'to prevent the building up of excessive pressures in the forward or back line, while at the same time maintaining a definite relation between their rate of For example, if the back pressure decreases, through increase in work resistance, the forward pressure will increase by a proportionate amount.

The functioning and adjustments for the leakage compensation means will be apparent, it' is believed, from a consideration of the principles discussed in connection with the preceding iigures. The valve A9 provides an mitial artificial leakage from the forward line into the back line to v'compensate for leakage effects under idling conditions. As heretofore noted, if these initial leakages into the back line are in excess of the sure lines.

leakages out of the back line,.aninitialv adjustment can be made at the sleeve member D of the valve S9 to provide the proper release of iiuid to the exhaust line 6| from the line 62 connected into the back line. In the present case the valve A9 is also so arranged that if the piston member 63 is adjusted to` the left a suicient distance it may optionally b employed to by-pass a selected iiow from the back line directly to the exhaust. The shuttle valve S9 differs from those in cir- Vcuits described previously in that its position for compensation of leakage under and during variable working conditions is made a function of variations in bot-h the forward and the back pres- The valve member 64 is subjected at the right end to the pressure of the back line, and at its left end to the pressure of the forward line byreason, of the pipe line connection 65. The spring 66 acts also in the same direction as the back pressure, the screw 61 being provided, as i-n previous cases, to vary the spring characteristics as the environment and conditions may require. 'Ihe artificial leakage through the valve is has a lateral opening 69 into the casing chamber.

With the initial balancing of leakages under idling conditions having been made through the valve A9 as described, variations of leakage to maintain a balance under variablev work resistances are then automatically effected through the variator S9. For example with an increase in the work resistance .the pressure in the back line will decrease, andas a result ofthe effect of the differential valve 5 I, the pressure in the forward line will increase by a proportionate amount. The change in pressure in the forward line, under the usual proportions adopted for the differential valve 5|, will be greater in actual pounds than -the change` in the back line. -As a consequence the Valve member 64 will be moved to the right in Fig. 9 to increase the leakage therethrough out of the back line and compensate for increased indicated diagrammatically at 5| 'in Fig. 9, may,

be conveniently associated in a single compact unit.' Such-a unit is shown in Fig. 10. a The fluid connections thereof andthe principle of operation is essentially that of Fig. 6 with the detail elements including pumps, valves, etc. forming the organization of Fig. 9 incorporated therein.

The valve unit has a main casing A15 within which is located the differential valve element 16, the normally fixed but adjustable leakage valve 11, and the shuttle valve S1 which includes the valve element 18 variable as Vto position under the infiuence of variable forward pressure and the spring 19. Forward pressure is directed to the piston face 8|), through the branch pipe 8| leading from the forward pressure line 82. 'I'he valve member 18 has a longitudinal bore 83, the left end of which communicates with lateral ports 84 and vthe right end with -the chamber 85 leading ofthe spring 19, both in the manner and for the purpose heretofore described in connection with the various specific circuits, including thatof Fig;

ure. 6. 'I'he sleeve 90 forming the -nut for the 75 nature.

, screw y89 is made of lsoft metal and provides pack- 'valve 18r through port |00 and connected also to the chamber 93 through the port 94. Flow to the exhaust occurs through the passages B4 and 83, chamber 85 and exhaust pipe line 86. The adjustable valve 11 corresponding to the valve A5 of Figure 6, inv the position shown, serves to permit a leakage there-across from the forward line to th'e back line. This occurs through the fluid passages .consisting of the branch line 95, the annular channel 96 in the block 96, annular channel 91 in the sleeve 91%l of valve 11, lateral openings 98 in said sleeve, and through chamber 99 connecting with the chamber 93. For unusual conditions the valve member 11 may be adjusted to the left whereby fixed leakage occurs from the back line through the'opening m2 from the chamber 93, into the chamber |03, through port |04 and out through the pipe line |05 to the reservoir.

In this unit construction o-f Fig. 10 the differential valve means is shown in a specific form differing somewhat from that shown more or less diagrammatically in the various other figures. In this form the valve element 'I6 is urged in one direction by the spring |06 varied as to tension through adjustment ofthe screw |01. In opposition to the spring, a plunger |98, slidable in the sleeve |09, is .subjected on the piston face to the back pressure which has access thereto through the chamber 99. 'Ihe disk which may be integral with the plunger |08, bears against slidable pins ||2, (only one being shown), the opposite ends of which are urged against the valve element 16. The pressure from the forward line is also imposed on the valve'member 16 through fluid entering the bore ||3 leading from the forward pressure branch line 95. Thechamber which contains the spring |66 and the sleeve ||4 is, as heretofore noted, connected to the exhaust line |05, Valve 16, therefore, constitutes a relief outlet for the forward pressure line. A

It will be noted that increasing `pressures in either the back line or forward line tend to open the valve, and if either become excessive, such opening will occur, and pressure in the forward line relieved, which necessarily` simultaneously relieves pressure in the back line. Also, as a characteristic of the valve, if the back. pressure decreases, through e. g. increase in work resistance, the forward pressure will increase by a proportionate amount. The movable element 16 is, it will be noted, exceptionally light and. as a matter of fact, will be responsive to rapid fluctuations in the pressures in the lines andmaintain a certain relation .between the` rate of change of pressure in the back line and thc rate of change of pressure in thc forward line, in addition to relieving any excessive pressure in the forward line.

Negative work resistance In perhaps the majority of cases power devices operate against a resistance which is variable but continuously positive. The treatment of this invention, in connection with particular circuits, has been more or less limited in the foregoing applications to environments of such However.v such conditions arey by no means universal; but are found to be the opposite in many cases. In other words, a power device may, through a part, or all, of its cycle, be

subjected'to a negative resistance inJwhichsome external force is imposed on the movable ele-l cally different problems of compensation for leakages. It will be shown, however, that the present invention is based on fundamental principles remarkably adapted to cope with such reversal of characteristics.

In contemplation of the objects of this description and illustration to reveal the general adaptability of the invention, a milling machine has been selected as being a device which involves the varying and opposed operating characteristics noted.

When themachine is set up so that the cutter is operating with thefeed (downward or hookinout) the tool has a tendency to assist in the propulsion ofthe table. The Work resistance then becomes negative in its effect upon the forward pressure; and the back pressure, instead of being the lower of the two, becomes the higher pressure. When the machine is entirely 'free of resistance, including that of friction, the pressures on opposite sides of the piston approach each other in value and for the purpose of illustration may be assumed to be, for a specific example, as 400 lbs. per square inch. As soon as the work is engaged by the cutter, the cutter itself exerts a mechanical urge on the table in the same direction as that of the hydraulic feed equal to, let us say 500 lbs. per square inch of piston area. It the system is such that the forward pressure is maintained at a constant value, the forces now tending to propel the table are 400 lbs. hydraulic pressure plus 500 lbs. me-

Opposed Hence, with It may be here stated that the values above mentioned are illustrative only, and under the .simple conditions mentioned the forces might tend to'rise' to much higher values and it has been found desirable in many instances to introduce into the system a device for automatically'adjusting, or partially equalizing,the o'pposed hydraulic values relative to eachother, and in proportion to the work resistance. Such a device may assume the form of the differential valve 5| of Fig. 9. Irrespective, however, of what reduction of total .pressures is effected there will necessarily remain a preponderance of pressure in' the back line under conditions of Aa negative cut to balance the pulling. effect of the cutter. The net result may be a pressure difference of 500 lbs., orvery much higher, which causes a leakage of uid, in this case, fromthe back pressure line to 'the forward pressure line with a consequent `increase in rate of feed over the indicated setting. 'This leakage may be aptly termed an advancing leakage in circuits where the rate is controlled through regulation of the discharge.

than the lower pressure forward line.

ing fluid into the rate control line of a discharge regulated type system, and an extraction of fluid from the rate control line in the case of a supply regulated type of system. In either type of circuit the back pressure must necessarily be higher than the forward pressure.

In the discharge regulated type of circuit, where an injection of compensating fluid is required, a source thereof must be sought other In the specific hydraulic system described herein it is convenient and desirable to derive the balancing high pressure fluid from the high pressure booster pump Bo previously referred to. i

Fig. 11 illustrates somewhat diagrammatically how' this may be effected. A valve F is shown as connected with the discharge side of the high pressure pump Bo by means of the conduit |20. This control valve comprises a casing member f in which there is slidably mounted a Valve piston f1, one side ,f2 of Which is acted upon by the back pressure fluid supplemented by the value of an adjustable spring f3; and the other side f4 of which is subjected/to the pressure of the uid from the pump B0. plunger is tapered slightly and cooperates with .a port f5 which communicates with the conduit |2|. This last mentioned conduit connects with the forward pressure line as well as with the reservoir through the differential relief valve |22. Branch line |23, connected to the back pressure line |24, subjects the side f1 of the plunger to the back pressure. A branch line |20a connects the super pressure line |20 with a leakage control valve G which is constructed similar to the variator S3, S4 etc. hereinbefore described in connection with other figures, except that in Fig. 11, the variator G is responsive to variations in the back pressure and is used to control both in and out leakages. Thus, the super pressure in the branch line |20 will always be greater than the back pressure in line |23 by a constant amount, to wit: the unit value of the spring f3 of the regulating valve F, thereby avoiding even the slight deviation from exactitude of balance for all working pressures, which might otherwise obtain with a simple conical valve.

In its modified form the variator G comprises` a casing |25 which, forconvenience of manufacture. is provided with an apertured sleeve member |26. Within the sleeve member |26 is slidingly fitted a piston valve element 21 having reduced portions |28 and |29 that cooperate'with the holes formed in the sleeve, as will later be explained.

An adjustable spring |30 exerts a force on one end of the valve plunger in opposition to the pressure of the fluid acting in the chamber g8. In this instance, the chamber gs is connected to the back pressure in line |24. and any variation, therefore, in this pressure immediately causes the valve plunger |21 to take up a new position of equilibrium.

The super pressure from the pump Bo enters the valve through the line |203, passes the resistance presented by the tapered portion |20 of the The end f4 of the valvevalve element |21 and then enters the back pressure line |24. In this way of balancing retarding leakage in to the back pressure line is effected, and in amounts proportional to the value of the negative work resistance. As the mechanical .forward urge on the table increases, the back pressure increases and the greater will be the natural leakage from the back pressure lines to the forward pressure lines and, therefore, the valve taper |28 is so related that an increase in back pressure decreases the resistance at |28 permitting an increase in flow from super pressure to back pressure to compensate for the natural leakage out of the back pressure lines. The value of the spring |30 and the number of active coils thereof is, of course, adjusted' to suit the leakage factor of the particular machine.

The valve G, however, serves also to regulate the artificial out leakage when cutting against the feed, at which time the back pressure is lower than the forward pressure. This is effected/in substantially the same manner as heretoforeexplained in connection with other gures, but will be restated here. A conduit |3| connecting with the back pressure line |24 conveys fluid to one of the openings in the valve sleeve adjacent the tapered portion |29 formed on the valve element |21. When the work resistance is negative the line |3| will be completely closed, but when the resistance is positive the super pressure line |20a will be completely closed and line |3| opened more or less, depending upon the adjustment of the spri ng |30 and the value of the back pressure.` When back pressure line |3| is opened, uid passes or is bled out of the back pressure lines in amounts suflicient to balance the retarding in leakage. This artificial out leakage is controlled by the resistance at |29 of the Valve G, and passes directly to the reservoir through the line The valve G is likewise adapted to be adjusted to provide an initial balancing in leakage when the machine is idling, this adjustment being effected as in previous cases through the medium of the adjusting screw D, the turning of which moves the valve element |21, spring 30 and screw |33 as a unit relative to the holes in the valve sleeve |26, and in this way the initial opening at |28 or |29 of the valve may be adjusted or varied to suit the leakage requirements of the particular machine under idling conditions. After this adjustment has been made the screw |33 is actuated to vary the number of active coils in the spring member |30, thereby to regulate the eiect on the valve plunger of variations in the valve actuating pressures. It is to be noted in general that the adjusting screw D can be employed to adjust for variations in natural leakage in different machines under conditions of positive cut; and the screw B of the valve F then utilized to adjust the leakage characteristic of the mechanism when the machine is operating under conditions of a negative cut.

By. reference to circuits heretofore described it will be apparent that the valve G can alternative- 1y be made responsive to variations in forward pressure as a means of varying the amount of the compensating fluids.

F. g. l2 shows another type circuit derived from an application of the principles of our invention, this being a circuit which, like that of Fig. 1l, functions to compensate for leakages under conditions of both positive and negative work resistance.

The mechanism of this circuit includes the various pumpsvand main distributing valves of the circuits previously described. In addition the system is provided with valve R which may be an ordinary relief valve which permits the pump Bo to discharge into the forward pressure line |35, and provides a supply of uid under super pressure in the -line |36 made equal to, or slightly greater, through adjustment of spring |31, than the maximum pressure ever attained in either the forward or back line.

A calibrated resistance coil |38 is provided in the super pressure line |36 which is connected to a branch |39 of the back pressure line |40 and permits a small injection of fluid into the back line which, it will be seen, varies in amount inversely as the back pressure. Compared with the work resistance the amount will vary directly as the positive Work resistance, and inversely as the negative work resistance.

A valve |4| is also inserted in the circuit provided With an adjustable, but normally fixed, ow opening connecting the forward line to the back line. 'I'he flow through valve |4 it will be noted, may be in either direction dependent upon the relative pressures on opposite sides of the power piston. A specific characteristic of this system which differs somewhat from the others given is that, through valve |4|, the total of the leakage areas, between forward and back pressure lines, is made a constant value on all machines. Setting the valve under idling conditions, the leakage value is increased throughl proper opening of valve |4| to a value equal to, or slightly greater than the highest'value, when idling, ever encountered on any machine of the type for which it is designed and to which the system may be applied. The variator S12, shown as movable in response to changes in forward pressure, permits a Variable escapement of fluid from the back pressure line |40 to the reservoin/ The resistance element |38, providing an injection of fluid into the back line, is so chosen 0r adjusted that, under the condition of maximum negative work resistance-when the back pressure is a maximum and the forward pressure a minimumthe summation of the le'akages will be zero. In other words, the natural leakages out, added to the articial leakage out through valve |4| will equal and balance the leakages in through the element |38. The valve 'S12 will, at this point, be substantially closed. In a system thus arranged and adjusted the resultant effective leakage (summation) `wi1l have a definite, fixed value for any specific work resistance and temperature on any machine of the same type, regardless of the natural leakage characteristic of the particular machine.

The variation in leakage, produced by variations in working resistance and corresponding variations in pressure in the forward and back pressure lines is compensated for by Variations in the opening of thevalvermember |42 of the variator S12. As heretofore noted, in the lcase of the back pressure, the pressure will` Vary inversely as the work resistance; whereas, the forward pressure, on account of the action of the differential valve |48, will vary directly as the work resistance. Either the forward or the back pressure may, therefore, be utilized as a means for varying the opening of the compensating variator S12 in accordance with the work resistance. In the system of Fig. 12 th'e forward pressure has been chosen for this purpose. A branch line |43 conducts fluid from the forward line to act on the piston |44 in opposition to the spring |45.

Assuming the valve |42 to be set at zero opening under conditions of maximum negative work resistance-When the forward pressure is a minimum under conditions of maximum positive work resistance. The area of valve flow opening for a given variation in pressure is, ofcourse, a function of the valve contour or slope, and of the spring resilience. The desired values of these properties may be computed or determined by experiment. The screw |46 provides a means of adjustment in each machine.

Fig. 12 indicates the valve portion a straight slope which may be sufficiently accurate as a practical matter in many instances. However, it is to be noted that a variation of fluid by-passed is produced, not only by a variation in position of the valve, but also that the pressure difference across the valve varies, and the discharge must be expressed algebraically in terms of the second order as previously pointed out, which.

graphically results in a parabolathe necessary contour of the effective end |41 of the valve for extreme accuracy. It will be seen that the last described system has an advantage with respect to the variator Valve in that the contour of the element |41 thereof may be made continuous as distinguished e. g. from the double Valve of Fig. 1l.

The specific systems disclosed herein illustrate the principles of this invention and enable one, it is believed, by the application of such principles to compensate for the leakages occurring in other specific types. This may, in certain instances, require the combination of two or more of the elementary circuits and means dealt with herein. Such, in fact, is the case with respect to the circuits of Figs. l1 and 12 herein. In making such combinations, a convenient method e. g. of determining the required contour for the variator valve, where the systems become more complex as in Fig. 12, is to determine the contour for one type of circuit or fluid compensation, and then that of the other circuit and combine the two contours into one continuous slope.

It may be of interest to illustrate the opera; tion of the above system by examples of the relative leakages and pressures which experimental data, computation, and plotted curves indicate to be typical of a circuit of a specic type of hydraulic power system coming within the principles outlined in the foregoing description. It is to be understood that the values related are intended to be representative only and may actually approach' those given only in very special cases. In a system similar to' that of Fig. 12 applied to certain sized milling machines, data selected shows that the pressure on the forward side of the piston may range from 880 lbs. per square inch to lbs. per square inch as the work resistance varies from a maximum positive to a maximum negative under conditions, in the latter extreme, of a cutting force acting in the direction of movement; Simultaneously the back pressure may vary in inverseproportion from lbs. per square inch to 400 lbs. per square inch. The rate of change of forward pressure with respect to change of back pressure is, of course, determined primarily by the ratio of the effective piston areas |48a and |48b of the differential valve |48. In this case this ratio is assumed to be 3 to 1. At some point the opposed pressures in this type of system will be equal, which in the present casev will be in the neighborhood of 325 lbs.

the determination of their value at selected points,

may be graphically represented on a chart,.having the respective pressures noted above as ordinates along one axis.

A chart thus prepared affords a means of determining the respective leakage values at any value of piston pressure (work resistance); andas an example a chart exemplifying the conditions of a system corresponding to that of Fig. 12 .and having the piston pressures noted' above shows the following: At idling condition the forward pressure is 400 lbs. and the back pressure is 300 lbs. producing a differential pressure of 100 lbs. If

the relief Valve R has been set to produce a constant pressure of 880 lbspper square inch in the line |36, then the pressure difference across the coil |38 will be 580 lbs. per square inch. The

leakage then into the back line across the piston.

and including the opening through valve MI, as part of the fixed natural leakage areas, is shown to be 5 cubic inches per minute.

S1? providing a balance in proportion to variations` in pressure produces, at this point, a leakage out of the back line of 27 cubic inches per minuto. The sum of the out-leakages is, therefore, 33 cubic inches per minute, which balances the in y leakages.

back pressure is decreased to 140 lbs. the differ- Taking an extreme point, in the direction of maximum positive Work resistance, where the forward pressure is increased to 880 lbs, and the ential pressure across the piston will then he increased to 740 lbs.; and the leakage into the back line across the piston, and through the valve |4| and any other susceptible areas has increased proportionately from 5 to 37 cubic inches. The leakage through the coil |38 has similarly increased, in direct proportion to the change in pressure difference across it, from 28 to 36 cubic inches, producing a total leakage into the back line of 73 cubic inches per minute. From the curve of leakage values through valve S12 it appears that this has increased proportionatelyto the increase on piston |44 from 27 cubic inches to a value of '70 cubic inches; and

. the higher, this leakage -is out of the back line, vand into the forward line, the curve for this leakage having crossed the base o-r zero line for out-leakage. vscription of Fig. 12 that the valve S12 at this To this is added a leakage of 28 cubic inches through `the coil |323 fallen to 23 cubic inches in-leakage balancing the I It will be recalled from the depoint was adjusted to the zero value, just at the point of opening.

Another critical and interesting point to be noted on a prepared chart of this nature, is that where the pressures in the back and forward lines are equal. it can be determined by computation or inspection of the chart that this point occurs at the piston pressure of 325 lbs. i The leakages then will be articial out-leakages through valve S12 andr natural out-leakages through the main valves, etc., to the reservoir; and in-leakages through the resistance element |38. No leakage, of course, occurs across the piston or valve |4I. Y

The natural leakage points in any particular type of circuit may consist of various joints, distributing valves, pistons, etc., which form the physical or mechanical components thereof, and in referring throughout the foregoing to natural in, or out-leakages, it is intended that these are merely illustrative of the many possible sources and not limited-simply to the piston or specic element mentioned. The particular points of natural leakage are it will be understood, the various components which in their sum total constitute the machine factor, and once having been experimentally determined upon, can be initially compensated for under a specic condition, and since they `thereafter all simultaneously vary in direct or inverse proportion to variation in pressure this Asame variation can be utilized to regulate a further variable artificial leakage to maintain a balanced system under all conditions. v

On the relations noted above l It may be noted, and it is here desired to particularly emphasize, that the term work resistance, as employed throughout the specification and claims, is intended to mean the resultant of the mechanical forces tending to either urge or restrain the movement of the translatable element; and may be, as has been' explained, either positive or negative in its eiect. The Work resstance is e. g. negative when it tends to assist in the normal movement; and positive when v'it tends to restrainsuch movement. If neither condition is present then the work resistance`becomes-zero in value. Algebraically then the term Work resistance? may be zero, a negative quantity, or a positive quantity.

Without further analysis, the foregoing wi so fully reveal the gist of this invention that others cam-by applying current knowledge, readily adapt it for various utilizations by retaining one or more of the featuresv that, from thev standpoint of the prior art, fairly constitute es'- sential characteristics of either the'generic or` specific aspects of this invention and, therefore,

such adaptations should be, and are intended to be, comprehended within the meaning and range of equivalency of the following claims.

We claim:-

v1. A hydraulic system combining a motor; a

source of vhydraulic fiuid supply for said motor;

rate of movement thereof; and means providing.

leakages. .The natural' leakage out to the reservoir-an artificial leakage to balance the natural leakhas increased to 8 cubic inches. The total outleakage at this point then is 23 cubic inches. Checking our curve for thev ow through the resistance |38; it appears that this value has ages of. said rate control line.

2. A hydraulic propulsion means combining a hydraulic motor; a fluid rate control line thereproviding an enforced artificial leakage of hydraulic fluid with respect to said line to compensate for the natural leakage of said line.

3. An hydraulic motor; an hydraulic rate control line governing the speed of operation of said motor, said control line being subject to natural leakage normally tending to alter the speed of said motor; and means connected with said control line to provide an artificial leakage tending to retard or `advance thespeed 'of said motor, conversely as the resultant natural leakage of said line tends to advance or retard respectively the speed of said motor.

4. A hydraulic power motor for machine tools; a rate control line including means therein for regulating the discharge from said motor to thereby regulate its speed, said line being subject to natural leakage of fluid thereinto in excess of any natural out-leakages and means for artificially extracting hydraulic fluid from said line to compensate for the resultant natural leakages into said rate control line and thereby maintain a balancing of the leakages.

5. A hydraulic power mot-or for machine tools; a rate control line including means therein for regulating the discharge from said motor to thereby regulate its speed, said line being subject to natural out-leakages in excess of any natural in-leakages; and means for articially injecting hydraulic fluid into said line to compensate for the resultant natural out-leakages of said line to thereby maintain a balancing of the leakages.

6. A hydraulic propulsion system for machine tools combining an hydraulic motor; a hydraulic rate control line connected thereto; means in said v line for regulating the ow of liquid therein and thereby the speed of said motor; said line being subject to natural leakages which result in variation of` the speed of said motor; and means connected to said control line providing an artificial leakage to balance the resultant natural leakage thereof.

'1. An hydraulic propulsion system combining an hydraulic motor; a hydraulic rate-control line connected thereto; means in said line for regulating the flow of liquid therein and thereby the speed of said motor, said line being subject to natural leakages which result in variation of the speed of said motor; means connected to said control line providing an artificial leakage opposed to the resultant of said natural leakages to compensate therefor; and means for automatically varying said artificial leakage as said resultant leakage varies under changes cf pressures resulting from variations of the work resistance thereby to maintain a balanced leakage under all normal conditions of operation.

8. An hydraulic propulsion system for machine tools combining an hydraulic motor; an hydraulic fluid line for the discharge from said motor; means in said line for regulating said discharge and thereby the speed of said motor, said line being subject to natural leakages which result in variation of the speed of said motor; and means connected to said discharge line providing an artificial leakage to balance the resultant natural leakage thereof.

9. An hydraulic propulsion system for machine tools combining an hydraulic motor; an .hydraulic fluid line for the discharge'from said motor; means in said line for regulating said discharge and thereby determining the speed of said motor, said line being subject to natural a fluid regulating device in said line and means' leakages which affect the speed of said motor; means connected to said discharge line providing an artificial leakage to compensate for the resultant natural leakage; and means for automatically varying said artificial leakage as said' resultant natural leakage varies with variations in work resistance and corresponding variations in pressure in said system, whereby a balancedleakage is maintained for all values of work resist-A ance.

10. An4 hydraulic propulsion motor for machine tools; a hydraulic fluid rate control linel therefor including means therein for regulating the supply to said motor and thereby the speed of said motor, said line being subject to natural leakages which result in variation of the speed of said motor; and means connected to said control lineproviding an artificial `leakage to balance the resultant natural leakage thereof.

l1. An hydraulic propulsion system for machine tools combining an hydraulic'motor; an hydraulic fluid supply line therefor including means therein for regulating A the supply to said motor and thereby the` speed of the latter, said line being subject to natural leakages which result in variation of the speed of said motor; means connected to said supply line providing an artificial leakage opposed to the resultant natural leakage to compensate therefor; and means for automatically varying saidartiflcial leakage as said resultant natural leakage varies to maintain a balanced leakage for all variations of work resistance and thereby of natural leakages.

12. An hydraulic propulsion system for machine tools combining an hydraulic motor; an hydraulic fluid supply line therefor; means in said line for regulating the supply to said motor and thereby the speed of the latter, said line being subject tonatural leakages of which the total out-leakages are lin excess of all in-leakages whereby a retarding effect is produced on the speed of the motor; and means connected to said supply line for artificially injecting fluid to cornpensate for the Yresultant natural out-leakages.

13. An hydraulic power system combining an hydraulic motor; a fluid line connected thereto; a regulating device in said line; said line being subject to natural leakages thereby affecting the rate of operation of said motor; initial articial leakage means connected to said linefor providing an artificial leakage of hydraulic fluid to compensate for the resultant of the natural leakages under a selected work resistance with corresponding pressuresln said system; a variable artificial leakage compensating means connected to said line; and means for controlling said variable leakage connected to a point in said system subject to variations of pressure in accordance with variations of said work resistance, said variable leakage being adapted thereby to compensate for the variations in natural leakage and said initial leakage means resulting from variations in Ipressure in said system as the work resistance varies from said selected value.

14. An hydraulic power system, said system being subject under varying work resistances to variations in pressures and to corresponding variations in natural leakages; means providing an artificial leakage operative under a selected work resistance to balance the resultant of the natural leakages; and means for automatically varying said artificial leakage to maintain a balance of leakages as the pressures in said system vary under variations in work resistance.

15. An hydraulic power system combining an hydraulic motor, said system being subject, under .t0 regulate the flOW 0f ccmpenSating fluid through varying work resistance, to variations in pressure Said Valve.

and corresponding Variations in natural leakages A mechanism fOr ccmpensating fOr the affecting the rate of operation of said motor; effects of. leakage in an hydraulic mOtOr Submeans connected in said system for providing an je'cted to variable loads and in which the natural articial leakage compensating for the resultant leakage 0f fluid therein Produces VariatiOnSin the of said natural leakages when said motor is oprate of movement ofthe mtcr cQmbining, a Valve erating under idling conditions; and means' for,v means, communicating With a Source. 0f fluid automatically varying said articial leakage to Pressure and Said 11101301' fOr Providing a flOW 0fmaintain a balanced leakage as said natural leakcompensating fluid t0 balance the natural leakages vary under varying pressures resulting from ages; and means responsive to variations in the variations in said work resistance. pressure in said motor for varying the effective- 16.' An hydraulic system combining an hy- `neSS 0f Said Valve means. draulic motor; hydraulic uid connections there- 21- An hydraulic SYStem .combining a OrWard -to including an hydraulic fluid rate control line; Pressure line and a back pressure line; an hya regulating device in said control line, said sys-- draulic mOtOr 0f the Piston and cylinder type c011- .tem being subject to variations in pressure with nected with said lines and in which there is a leakages vary under changes in pressures resultcorresponding variations in natural leakages a'fnatural leakage 0f uid from One VSide 0f Said DiS- fecting said control line and thereby the rate of ton to the other side tending to vary the rate operation of said motor; means connected with 0f movement 0f the mOtOr; and means including said control line providing a compensating leakan escap'ement device for providing for an arage to balance the resultant of said natural leaktiflcial balancing leakage 0f a magnitude Subages when said motor is operating under idling stantially equal t0 the natural leakage but Oppoconditions; and means for automatically varysite in its eiect upon the rate of movement of ing said compensating leakage as said natural said motor. y

22; A n hydraulic system combining a leaky ing from changes in Work resistance to thereby motor of the piston and cylinder type; conduits maintainl a balance between the leakages for all connected with said motor for conveying fluid conditions of operation. theretoA and therefrom; means for varying the 17. Anv hydraulic system combining an hyrate of flow through one of said conduits thereby draulic motor; hydraulic fluid connections thereto vary the rate of movement of `said motor; to including an hydraulic rate control line; a leakage compensating means for said motor; and regulating device in said control line, said system means automatically responsive to variations in being subject to'variations in pressure'with corthe fluid pressure in the conduit adapted to responding Variations in natural leakages aiiectconvey fluidlfrom the said motor for controlling ing said control line and thereby the rate of opthe eiectiveness of said leakage compensating eration of said motor; means connected with said means. control line providing a compensating leakage 23. An hydraulic system combining a` motor to balance the resultant of said natural leakages normally subject to natural leakages of the hywhen said motor is operating under idling condraulic fluid affecting its rate'of operation; fluid ditions; a pressure responsive device, connected conduits connected with said motor; mechanism in said hydraulic system at a point which varies for controlling the ow of fluid through one of in pressure with Variations in work resistance, said conduits thereby \to vary the rate of movefor controllingsaid compensating leakage means ment of said motor; means for counteracting the to maintain a balance of leakages in lsaid control effects of natural motor leakages on the rate of line for all variations in pressures resulting from movement thereof; and means automatically revariations in Work resistance. sponsive to Variations in one of the factors caus- 18. An hydraulic power system combining an ing motor leakage to vary the action of said counhydraulic'motor subject 'to variations of forces teracting means.

Jimpressed thereon in its operation; an hydraulic 24. A mechanism for compensating for leakhuid rate control line for said motor including ages normally occurring in an hydraulic motor v aregulating device therein, said line being subject thereby' to maintain a predetermined rate of to variable natural leakages aS the preSSureS in movement thereof. irrespective of variations in said system vary with the variation of forces on pressure values in the motor combining, a variasaid motor; means connected to control line proble orice valve means in liquid communication viding a compensating leakage to balance the re' with the uid in said motor and adapted to control.4

sultant ofthe natural leakages at a selected cona flow of compensating uid therethrough to baldition of operation` with corresponding pressure ,ance the eiect of the normal leakages; and variations in the system; and means for varying means for varying the effectiveness of said valve the compensating leakage as the natural leakage -means in accordance -with said variations in presvaries under varying pressures in the system resulting from variations in the forces on said motor, to thereby maintain the leakages balanced under all conditions.

sure values to maintain said balance under varying physical conditions.

25. A device for compensating for leakages normally occurring in an hydraulic motor', combining 19. A device for counteracting the effects of a valve mechanism for' causing an artificial leakleakage across the piston of a piston and cylinder ageto occur to balance the effect of the normal mechanism combining, a valve mechanismhaving leakage; and means responsive to variations in an adjustable valve element therein for controlthe uid pressure acting on one side of the piston ling a flow of uid therethrough; fluid connecof said motor` to vary the action of said valve tions between said valve mechanismand the uid-mechanism.

in said cylinder and between said valve mecha- 26. Anhydraulic propulsion system for machine nism and another source of fluid; and means tools combining an hydraulic motor; an hydraulic responsive to variations in the pressure of the` iiuid supply line therefor; an hydraulic liuid disrluld in'said last named uid connection to adcharge line for' said motor; Ameans inone of said just the position of said .valve element thereby lines for lregulating the ow of uidtherein and thereby the speed of said motor; said system being subject to in and out .natural leakages which result in variations inspeed of said motor; and means connected to one of said lines providing an artificial leakage opposed to the resultant natural leakage to compensate therefor, said articial leakage being subtraetive when the natural in'leakages exceed the natural out-leakages and additive when the natural out-leakages exceed the natural in-leakages; and means automatically varying said artificial leakage as said resultant natural leakage varies to maintain a balanced leakage under ail conditions of pressure and natural leakage.

HANS ERNST.

BERNARD SASSEN. 

